In a typical AC power distribution system in a residential or a small business building, an array of electromechanical circuit breakers protects various branch circuits of the electrical wiring. Such circuit breakers utilize a thermally operated switch which, upon reaching a predetermined temperature due to excessive current passing therethrough, will "trip" and open the circuit connected to the switch.
Improved circuit breakers providing very rapid trip response and the ability to monitor circuit conditions and store data related thereto are disclosed in U.S. Pat. No. 4,949,214, entitled "TRIP DELAY OVERRIDE FOR ELECTRICAL CIRCUIT BREAKERS" issued to George A. Spencer on Aug. 14, 1990, an assignee of the present U.S. patent application, and in U.S. Pat. No. 5,875,087 entitled "CIRCUIT BREAKERS WITH INTEGRATED CONTROL FEATURES", issued to Spencer, et al. and assigned to the assignee of the present application, which patents are incorporated herein by reference. The improved circuit breakers disclosed therein include an array of trip profiles tailored to the current draw characteristics of the various kinds of devices which may be connected to the AC power line branch circuit protected by the circuit breaker. These trip profiles, which are dynamically changeable, determine the current versus time configuration of the particular circuit breaker. Such improved circuit breakers overcome the principal disadvantages of the conventional thermally operated circuit breakers, including, for example, slow response time, inability of responding to differing in-rush current characteristics, inability of opening a circuit upon the occurrence of arcing (a potentially serious fire hazard), inadequate response to electrical stalling of motors connected to a protected line, etc.
Although the circuit breakers with trip delay override and the electronically controlled circuit breakers with integrated control features referenced above offer superior trip performance under a variety of load fault conditions, neither of the aforementioned advanced circuit breakers has the capability of storing substantial quantities of important system data obtained by the circuit breaker while monitoring the protected circuit, even for short interruptions of power.
Thus, there is a need for means to save the critical data in an electronic circuit breaker when the input power supply departs from normal specifications, in whatever degree and for whatever reason.